Viral Replication Process

As viruses are obligate intracellular pathogens they cannot replicate without the machinery and metabolism of a host cell. Although the replicative life cycle of viruses differs greatly between species and category of virus, there are six basic stages that are essential for viral replication.

1. Attachment: Viral proteins on the capsid or phospholipid envelope interact with specific receptors on the host cellular surface. This specificity determines the host range (tropism) of a virus.

2. Penetration: The process of attachment to a specific receptor can induce conformational changes in viral capsid proteins, or the lipid envelope, that results in the fusion of viral and cellular membranes. Some DNA viruses can also enter the host cell through receptor-mediated endocytosis.

3. Uncoating: The viral capsid is removed and degraded by viral enzymes or host enzymes releasing the viral genomic nucleic acid.